Standard Test Medium Research Articles

Electrodeposited zinc composite coatings with embedded carbon nanotubes – advanced composite materials for better corrosion protection

ABSTRACTThe aim of the present investigation was to demonstrate a preparation method for obtaining an electrodeposited composite zinc coating with incorporated carbon nanotubes (CNT). The composite coatings were additionally treated in a newly developed conversion solution based on a Cr(III)-containing compound. The surface morphology of the Cr(III) and non-Cr(III) samples was investigated with scanning electron microscopy (SEM), the metallographic structure with X-ray diffraction analysis (XRD) and the composition with X-ray photoelectron spectroscopy (XPS). Composite zinc coatings without and with the surface conversion film (CF) have been investigated in a standard test medium of 5% NaCl solution by use of potentiodynamic polarisation (PDP) curves, electrochemical impedance spectroscopy (EIS) and polarisation resistance (Rp) measurements. The results obtained show the synergistic effect of the incorporated CNT and conversion film for achieving better corrosion resistance of the system composite Zn/CF in aggressive medium containing chloride ions as corrosion activators.

Chromium hazard and risk assessment: New insights from a detailed speciation study in a standard test medium.

Despite the consensus about the importance of chemical speciation in controlling the bioavailability and ecotoxicity of trace elements, detailed speciation studies during laboratory ecotoxicity testing remain scarce, contributing to uncertainty when extrapolating laboratory findings to real field situations in risk assessment. We characterized the speciation and ecotoxicological effects of chromium (CrIII and CrVI ) in the International Organization for Standardization (ISO) medium for algal ecotoxicity testing. Total and dissolved (< 0.22 μm) Cr concentrations showed little variability in media spiked with CrVI , whereas dissolved Cr concentration decreased by as much as 80% over a 72-h time period in medium amended with CrIII . Analyses by ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) highlighted the absence of redox interconversion between CrIII or CrVI both in the presence and absence of algal cells (Raphidocelis subcapitata). Furthermore, the concentration of ionic CrIII dropped below detection limits in less than 2 h with the corresponding formation of carbonate complexes and Cr hydroxides. Precipitation of CrIII in the form of colloidal particles of variable diameters was confirmed by nanoparticle (NP) tracking analysis, single particle ICP-MS, and single particle counting. In terms of time-weighted dissolved (< 0.22 μm) Cr concentration, CrIII was 4 to 10 times more toxic than CrVI . However, CrIII ecotoxicity could arise from interactions between free ionic CrIII and algae at the beginning of the test, from the presence of Cr-bearing NPs, or from a combination of the 2. Future ecotoxicological studies must pay more attention to Cr speciation to reliably compare the ecotoxicity of CrIII and CrVI . Environ Toxicol Chem 2018;37:983-992. © 2017 SETAC.

Correcting a Fundamental Flaw in the Paradigm for Antimicrobial Susceptibility Testing

The emergence and prevalence of antibiotic-resistant bacteria are an increasing cause of death worldwide, resulting in a global ‘call to action’ to avoid receding into an era lacking effective antibiotics. Despite the urgency, the healthcare industry still relies on a single in vitro bioassay to determine antibiotic efficacy. This assay fails to incorporate environmental factors normally present during host-pathogen interactions in vivo that significantly impact antibiotic efficacy. Here we report that standard antimicrobial susceptibility testing (AST) failed to detect antibiotics that are in fact effective in vivo; and frequently identified antibiotics that were instead ineffective as further confirmed in mouse models of infection and sepsis. Notably, AST performed in media mimicking host environments succeeded in identifying specific antibiotics that were effective in bacterial clearance and host survival, even though these same antibiotics failed in results using standard test media. Similarly, our revised media further identified antibiotics that were ineffective in vivo despite passing the AST standard for clinical use. Supplementation of AST medium with sodium bicarbonate, an abundant in vivo molecule that stimulates global changes in bacterial structure and gene expression, was found to be an important factor improving the predictive value of AST in the assignment of appropriate therapy. These findings have the potential to improve the means by which antibiotics are developed, tested, and prescribed.

Fate and Effects of CeO2 Nanoparticles in Aquatic Ecotoxicity Tests

Cerium dioxide nanoparticles (CeO2 NPs) are increasingly being used as a catalyst in the automotive industry. Consequently, increasing amounts of CeO2 NPs are expected to enter the environment where their fate in and potential impacts are unknown. In this paper we describe the fate and effects of CeO2 NPs of three different sizes (14, 20, and 29 nm) in aquatic toxicity tests. In each standard test medium (pH 7.4) the CeO2 nanoparticles aggregated (mean aggregate size approximately 400 nm). Four test organisms covering three different trophic levels were investigated, i.e., the unicellular green alga Pseudokirchneriella subcapitata, two crustaceans: Daphnia magna and Thamnocephalus platyurus, and embryos of Danio rerio. No acute toxicity was observed for the two crustaceans and D. rerio embryos, up to test concentrations of 1000, 5000, and 200 mg/L, respectively. In contrast, significant chronic toxicity to P. subcapitata with 10% effect concentrations (EC10s) between 2.6 and 5.4 mg/L was observed. Food shortage resulted in chronic toxicity to D. magna, for wich EC10s of > or = 8.8 and < or = 20.0 mg/L were established. Chronic toxicity was found to increase with decreasing nominal particle diameter and the difference in toxicity could be explained by the difference in surface area. Using the data set, PNEC(aquatic)S > or = 0.052 and < or = 0.108 mg/L were derived. Further experiments were performed to explain the observed toxicity to the most sensitive organism, i.e., P. subcapitata. Toxicity could not be related to a direct effect of dissolved Ce or CeO2 NP uptake or adsorption, nor to an indirect effect of nutrient depletion (by sorption to NPs) or physical light restriction (through shading by the NPs). However, observed clustering of NPs around algal cells may locally cause a direct or indirect effect.

Effect of Varying Physicochemistry of European Surface Waters on the Copper Toxicity to the Green Alga Pseudokirchneriella subcapitata

Most standard toxicity test results, used in present environmental risk assessment and water quality criteria (WQC) setting procedures are obtained with standard test media that are not representative for natural surface waters when metal toxicity modifying factors like pH, water hardness and dissolved organic carbon (DOC) are considered. The aim of this study was, using the green alga Pseudokirchneriella subcapitata, (1) to investigate the individual effects of Ca, Mg (the hardness cations) and pH on the toxicity of copper in reconstituted artificial test waters and (2) to study the copper toxicity in 13 spiked surface waters originating from different European eco-regions. Surface waters were selected such that a broad range of DOC (1.55-20.4 mg/l), pH (5.52-8.30) and water hardness (7-238 mg CaCO(3)/l) was covered. Tests in reconstituted artificial waters demonstrated that the 72 h-E(b)C50 (expressed as dissolved Cu) increased by about a factor of 3 when the Ca and Mg concentrations increased from 0.25 to 2.5 mM. When pH was increased from 5.8 to 8.0, dissolved 72 h-E(b)C50 decreased by a factor of 3. It is suggested that competition between Cu2+, Ca2+, Mg2+ and H+ ions at the cell surface are the most likely explanation for these observations. Dissolved 72 h-E(b)C50s in the natural surface waters varied between 32.0 and 245 mug Cu/l and were up to a factor 15 higher than the 72 h-E(b)C50 in standard artificial medium (16.5+/-4.8 mug Cu/l). Consequently, Water Effect Ratio's (WER, the ratio between the EC50 in natural water to the EC50 in standard test water) ranged from 1.9 to 14.8. Linear regression analysis revealed that higher E(b)C50 were significantly related to higher DOC-concentration of the natural waters (R2 = 0.69), but that water hardness and pH did not show a significant relation with copper toxicity in these surface waters. In European surface waters, a positive correlation is observed between water hardness and pH. As a result, hardness and pH effects on copper toxicity are counteractive in European surface waters, resulting in the highly significant relation between the 72 h-E(b)C50 and DOC-concentration. Normalisation of the obtained effect concentrations using a Biotic Ligand based predictive Cu-toxicity model revealed that variation in DOC and pH are mainly responsible for the observed differences of Cu-toxicity in natural waters.

Acclimation of Daphnia magna to environmentally realistic copper concentrations

It may be hypothesised that as the bioavailable background concentration of an essential metal increases (within natural limits), the natural tolerance (to the metal) of the acclimated/adapted organisms and communities will increase. In this study the influence of acclimation to different copper concentrations on the sensitivity of the freshwater cladoceran Daphnia magna Straus was investigated. D. magna was acclimated over three generations to environmentally relevant copper concentrations ranging from 0.5 to 100 μg Cu/l (copper activity: 7.18×10 −15 to 3700×10 −12 M Cu 2+). A modified standard test medium was used as culture and test medium. Medium modifications were: reduced hardness (lowered to 180 mg CaCO 3/l) and addition of Aldrich humic acid at a concentration of 5 mg DOC/l (instead of EDTA). The effects of acclimation on these organisms were monitored using acute mortality assays and long-term assays in which life table parameters, copper body concentrations and energy reserves were used as test endpoints. Our results showed a two-fold increase in acute copper tolerance with increasing acclimation concentration for second and third generation organisms. Copper acclimation concentrations up to 35 μg Cu/l (80 pM Cu 2+) did not affect the net reproduction and the intrinsic growth rate. The energy reserves of the acclimated daphnids revealed an Optimal Concentration range (OCEE) and concentrations between 5 and 12 μg Cu/l (0.5–4.1 pM Cu 2+) and 1 and 35 μg Cu/l (0.023–80 pM Cu 2+) seemed to be optimal for first and third generation daphnids, respectively. Lower and higher copper concentrations resulted in deficiency and toxicity responses. It was also demonstrated that up to 35 μg Cu/l, third generation daphnids were able to regulate their total copper body concentration. These results clearly indicate that bioavailable background copper concentrations present in culture media have to be considered in the evaluation of toxicity test results, especially when the toxicity data are used for water quality guideline derivation and/or ecological risk assessment for metals.

Accelerated testing of a filled polyester E-glass composite in acidic environments

This paper describes the results of an accelerated laboratory investigation to measure the rate of deterioration of a newly developed filled plastic composite exposed to acidic (sewage) environments. The specific objective was to compare the relative rates of deterioration of an experimental filled filament wound (FFW) polyester composite immersed in sulfuric (pH 2.23) and acetic (pH 2.22) acid environments at 45 °C. Deterioration was measured in terms of changes in wet specimen weight, loss in dried (soluble) material weight and mechanical properties, the extent of chemical dissolution, and the depth of penetration. Based on regression analyses of these parameters, it was found that the rate of deterioration was a function of the square root of immersion time. Deterioration of the FFW composite in acetic acid was 1.6–3.9 times greater than in the sulfuric acid environment. The loss in wet flexural properties and the dissolution behavior of aluminum trihydrate were not influenced by the type of acid environment. Based on the findings of this study, sulfuric acid is recommended as a standard laboratory test medium for fiberglass reinforced plastic composites used in construction of sewage facilities and pipelines where deterioration due to sulfur oxidizing bacteria is anticipated. Key words: accelerated, polyester, fillers, filament-wound, environment, acidic, durability, composite, septic tanks.

Alternation of the q-Switched Nd: YAG Laser and the cw Argon Laser for Tunneling through Organic Material

The rapidly alternating combination of Nd:YAG laser power of the optical break-down mode with cw energy of the argon laser ablates tissue. Blood agar provides a standard test medium as tissue substitute and permits to quantify the effect of various laser energy combinations to achieve optimal ablation. High wattage of the Nd:YAG laser provides destructive pressure that creates fissures which act as the light traps of a black body simulator for efficient cw argon laser energy conversion to pressure and kinetic energy. Within the fissure the deposited cw argon laser energy is directed by gradients toward the tissue surface so that deepening troughs or tunnels are formed by expelling tissue debris.

Exposure of phytoplankton to ekofisk crude oil

Solutions of Ekofisk crude oil in sea water were prepared by slow stirring for 21h in a closed system. Headspace and GC/MS techniques were applied to establish dose composition and levels. The standardized test medium produced in a closed system contained approximately 14 mg oil per litre and was dominated by low molecular weight aromatic hydrocarbons and phenols. The toxicity of the standarized oil-containing medium to three marine diatoms was studied in a cage culture turbidostat and by conventional batch culture technique. The three algal species differed in sensitivity to the oil compounds, but showed identical ranking in both test systems. Standardized test medium diluted to 50% with respect to oil content stopped the growth of the most sensitive alga, Skeletonema costatum. For comparison naphthalene was applied and gave 50 % growth reduction at a concentration of 400 μg litre −1. The growth of Chaetoceros ceratosporum was only slighty affected by the full strength standard test medium, which had no influence on the growth of Phaeodactylum tricornutum, the least sensitive organism. The presence of an oil layer on the surface of the standard test medium during the growth test greatly increased its toxicity and blocked completely the photosynthesis even of P. tricornutum after 4 days.

Histochemical Studies of Carboxylic Esterase Activity in Fasciola hepatica

A histochemical study has been made of the distribution of carboxylic esterase activity in adult Fasciola hepatica. By the use of specific substrates and inhibitors three distinct esterases have been localized in various tissues within the worm. In general, acetylcholinesterase activity is found in the tegument and neuromuscular tissues, nonspecific esterases in the reproductive structures, and a resistant-type indoxyl esterase occurs in the gut epithelium. The results are compared with biochemical findings and the role of carboxylic esterases in the liver fluke is discussed. The occurrence of carboxylic esterases in adult Fasciola hepatica was first reported by Bacq and Oury (1937) who demonstrated the presence of cholinesterase activity in extracts of the worm. Using whole fluke homogenates, Pennoit-de Cooman and van Grembergen (1942) found lipase activity and, in addition, confirmed the presence of a cholinesterase which has since been identified as a true (acetyl) cholinesterase (Chance and Mansour, 1953; Sekardi and Ehrlich, 1962; Frady and Knapp, 1967). Pantelouris (1967), using electrophoretic separation techniques, found a single main band of esterase activity in extracts of F. hepatica which was capable of hydrolyzing a number of carboxylic esters, and two slower bands when a naphthol ester was used as substrate. From spectrophotometric measurements the esterases were found to hydrolyze esters of long chain fatty acids more readily than those of either short chain fatty acids or of choline, and, further, the main band of activity was found to be resistant to known inhibitors of cholinesterase, such as eserine sulphate, as well as to a number of organophosphate compounds. It would seem therefore that F. hepatica contains at least three distinct carboxylic esterases, the most active of which is an organophosphate-resistant type. The present work represents a histochemical examination of carboxylic esterases in F. hepatica, including a study of the effect of inhibitors, in an attempt to locate sites of specific esterase activity within the worm and to relate the findings, as far as possible, to the known biochemical evidence. Received for publication 7 September 1967. MATERIALS AND METHODS Live specimens of F. hepatica were collected from the bile ducts of freshly slaughtered sheep, washed in Hedon-Fleig solution, and fixed for 2 hr at 4 C in 10% formalin containing 0.05 Mi sucrose and held at pH 7.2 with 0.15 M phosphate buffer. In most cases the worms were bisected transversely in fixative to aid penetration of the latter and facilitate subsequent sectioning. Following fixation each half worm was washed in three changes of buffer and frozen in 5% sucrose on a thermoelectric (Pelcool) freezing stage fitted to a standard rotary microtome. Sections (10 to 15 u thick) were cut using a mounted steel razor blade and transferred to glass slides and allowed to dry in air (1 to 2 hr). Alternatively, a number of sections were transferred directly to the incubating medium and free-floated. Sections were processed for esterase activity using standard techniques described in Pearse (1960). The following substrates, together with details of the incubation times and temperatures, were used: naphthyl acetate, propionate (30 min, 20 C), caprylate (12 hr, 20 C), naphthol ASacetate (6 hr, 20 C), and 5-bromoindoxyl acetate (3 hr, 37 C) for nonspecific esterases; naphthyl laurate, stearate (12 hr, 20 C), Tween 60 and Tween 80 (24 hr, 37 C) for lipases; and acetyl or butrylthiocholine iodide (6 hr, 37 C) for cholinesterases. In the case of the long chain fatty acid esters, where extended periods of incubation were needed, sections were transferred to freshly prepared media at 3-hr intervals. The effect of inhibitors on esterase activity (see Pearse, 1960) was studied by preincubating sections for 1 hr in a buffered solution of inhibitor followed by incubation in the standard test medium containing that inhibitor. The inhibitors are listed in Table I along with details of their molarity in the incubation mixture. Control slides consisted of sections exposed to distilled water at 60 C for at least 3 min prior to incubation or sections incubated in test media without the substrate. In all other details the inhibitor and control media were identical to the corresponding test series.